Subdomains and 1 Webspace for all okay?

Hey there,
I want to target some easy keywords. They aren't searched much so I don't want to buy an extra webspace and an extra domain for all sites.
My idea is to buy one domain that sounds good (e.g. "help.com") and make subdomains with my keyword.
Will that be not a bad thing? I'm sure that Google doesn't like something like that, but my competition isn't that hard so I wonder if I can neglect a different c-class IP and different domains.

Thanks
cable

As long as you aren't going apeshit with 1000+ subdomains all on one go you should be ok.